I'm gonna cover things like this in a "basics of the map editor". I guess I was thinking it was an intuitive thing, as it happened as a natural thing to me after I've played with the terrain tools.
Click and hold, drag up, and you will be planting loads of trees!
If you click and hold, then drag down, you will reduce the amount of trees in the selected area. That is, if it's already some trees there.
So stay tuned. I'll make a "Map Editor 101" kind of thing within a few days. I got work and a social life to take care of too, you know.
